XMPP is a messaging protocol. Jingle is a sub protocol used by XMPP to establish voice calls or transfer files. WebRTC is a Javascript API (there is also a library that implements this API).
You can use Jingle as a signaling protocol to establish peer-to-peer communication between two XMPP clients using the WebRTC API. This shows an example in Javascript that works in Chrome and Firefox (and Microsoft Edge if you only need sound).
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